It has been estimated that approximately 85% of the total cost of operating a conventional pump is attributable to energy consumption. Pumping systems account for nearly 20% of the world's electrical energy demand and range from 25% to 50% of the energy required by industrial plant operations.
Similarly, maintenance costs account for approximately 10% of the total cost of operating a conventional pump.
Pumping liquids against substantial hydraulic heads is a problem encountered in pumping out mines, deep wells, and similar applications such as pumping water back up, over a hydro dam during low energy usage periods, for subsequent recovery during high energy usage periods, and for run-of-the-river hydro power applications utilizing the potential energy of water in a standing column.
Several earlier patents attempt to provide devices which utilize a piston type pump where energy is recovered from a column of liquid acting downwardly on the piston, as the piston moves downwardly, to assist in subsequently raising the piston with a volume of liquid to be pumped upwardly. An example of such an earlier patent is U.S. Pat. No. 6,193,476 to Sweeney. However such earlier devices have not been efficient enough to justify commercial usage. In the Sweeney patent, for example, the efficiency of the apparatus is significantly reduced due to the upper piston 38 having the same cross-sectional area as lower piston 43. Thus the pressure of liquid acting upwardly on the lower piston 43 inhibits downward movement of the upper piston 38 under the weight of the liquid in the cylinder above.